1. Field of the Invention
The invention relates to a process for minimizing the concentration of toxic organic pollutants in the fly dusts of incineration plants, in particular waste incineration plants, in which, at time intervals, at least a part of the fly dusts produced in the incineration plant is recirculated to the incineration process.
2. Description of the Related Art
The toxic organic pollutants in the fly dusts are, in particular, polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), precursor compounds, that is to say precursors of PCDDs and PCDFs, for example mono- and dichlorobenzene, polychlorinated biphenyls (PCBs) and further compounds which are comparable in structure or activity. These organic pollutants are frequently described and quantified in summary form in the literature and emissions legislation using an internationally employed toxicity equivalent in ng per kg of fly dust (ng I-TEQ/kg). The I-TEQ here is based on an equivalent toxicity of the sum of a multiplicity of organic pollutants to the seveso dioxin 2,3,7,8-tetrachlorodibenzodioxin.
EP 0 862 019 A1 discloses recirculating at least a part of the fly dusts exiting from the incineration plant to the high-temperature region of the incineration plant in order to induce vitrification and sintering of the dusts, so that the products obtained by this process can be added back to the grate ash or used separately.
The amount of fly dust remaining can thereby be reduced. The fly dusts are obtained by cleaning the boiler or by removal from the filter systems and, when a grate firing is used, recirculated to the combustion chamber of the incineration plant above the combustion bed. This process does not take into account the presence of toxic compounds, for example dioxins or precursors.
DE 33 20 466 C3 also discloses recirculating fly dusts into the combustion chamber of an incineration plant. Here the fly dusts are chemically treated before the recirculation with the purpose of reducing the pollutants outside the combustion chamber of the incineration plant. Therefore a low-pollutant fraction of the fly dusts is recirculated which is then incorporated into the slag in a high-temperature process.